Effects of Culture Area,Stocking Density,and Shrimp and Fish Polyculture on the Cost Efficiency of Hard Clam,Meretrix meretrix,Culture: A Case Study of Hard Clam Farms in Yunlin,Taiwan          下载免费PDF全文

Jung‐Fu Huang  Ming‐Tao Chou  Jie‐Min Lee  Yung‐Hsin Cheng 《Journal of the World Aquaculture Society》2016,47(4):481-495

Using the hard clam farms in Yunlin, Taiwan as examples, this study analyzes the effects of culture area, stocking density, and shrimp and fish polyculture on the cost efficiency (CE) of hard clam farming. A data envelopment analysis (DEA) is used to estimate the farms' technical efficiency (TE), allocative efficiency (AE), and CE values. The findings show that the mean TE, AE, and CE values of hard clam farms are 0.74, 0.57, and 0.43, respectively. The TE value is higher than the AE value, which indicates that cost inefficiency is mainly attributable to poor AE. Tobit regression results suggest that there are positive relationships between CE and both culture area and operator experience. Hard clam stocking density and age of the operators have negative effects on CE. Hard clam culture areas larger than 2 ha and a stocking density of 1.1–1.2 million hard clams per hectare have higher CEs than smaller culture areas and smaller or larger stocking densities. The use of sand shrimp, white shrimp, kuruma shrimp, and grass shrimp for polyculture and the use of milkfish and silver sea bream for polyculture are both associated with high CEs.  相似文献   

转变兽药行政审批理念提高兽药行政审批效能     

贾幼陵 《中国兽药杂志》2007,41(5):1-4

兽药行政审批工作，是法律设定的具有强制力的政府行为，对管理相对人和生产者、畜产品消费者的利益影响重大，处理不好，很容易引发社会矛盾。兽药管理在管理制度、管理内容和管理形式上，与人用药品管理都有很多相似之处，国家食品药品监督管理局腐败案件的发生，给我们敲响了警钟。本文结合近年来兽药管理工作实践，借鉴发达国家的先进管理理念，从树立先进审批理念、严格审批程序和建立完善权力运行机制等3个方面着重阐述了兽药行政审批工作应坚持以科学发展观为指导，转变审批理念，完善审批程序，提高审批效能。  相似文献   

Characterization of aerosols containing microcystin          下载免费PDF全文

Cheng YS  Zhou Y  Irvin CM  Kirkpatrick B  Backer LC 《Marine drugs》2007,5(4):136-150

Toxic blooms of cyanobacteria are ubiquitous in both freshwater and brackish water sources throughout the world. One class of cyanobacterial toxins, called microcystins, is cyclic peptides. In addition to ingestion and dermal, inhalation is a likely route of human exposure. A significant increase in reporting of minor symptoms, particularly respiratory symptoms was associated with exposure to higher levels of cyanobacteria during recreational activities. Algae cells, bacteria, and waterborne toxins can be aerosolized by a bubble-bursting process with a wind-driven white-capped wave mechanism. The purposes of this study were to: evaluate sampling and analysis techniques for microcystin aerosol, produce aerosol droplets containing microcystin in the laboratory, and deploy the sampling instruments in field studies. A high-volume impactor and an IOM filter sampler were tried first in the laboratory to collect droplets containing microcystins. Samples were extracted and analyzed for microcystin using an ELISA method. The laboratory study showed that cyanotoxins in water could be transferred to air via a bubble-bursting process. The droplets containing microcystins showed a bimodal size distribution with the mass median aerodynamic diameter (MMAD) of 1.4 and 27.8 mum. The sampling and analysis methods were successfully used in a pilot field study to measure microcystin aerosol in situ.  相似文献   

Isotopic fractionation of stratospheric nitrous oxide     

YL Yung  CE Miller 《Science (New York, N.Y.)》1997,278(5344):1778-1780

We propose an isotopic fractionation mechanism, based on photolytic destruction, to explain the 15N/14N and 18O/16O fractionation of stratospheric nitrous oxide (N2O) and reconcile laboratory experiments with atmospheric observations. The theory predicts that (i) the isotopomers 15N14N16O and 14N15N16O have very different isotopic fractionations in the stratosphere, and (ii) laboratory photolysis experiments conducted at 205 nanometers should better simulate the observed isotopic fractionation of stratospheric N2O. Modeling results indicate that there is no compelling reason to invoke a significant chemical source of N2O in the middle atmosphere and that individual N2O isotopomers might be useful tracers of stratospheric air parcel motion.  相似文献   

基于鲁棒自适应控制策略的混合型步进电机低速伺服控制性能     

陈卫东  容启亮 《勤云标准版测试》2007,(1):8-16

针对混合型步进电机低速运行状态下脉动转矩较大的特点,应用鲁棒自适应控制策略来设计其低速伺服控制器,以实现高精度的跟踪控制性能.首先,根据混合型步进电机转矩形成的机理,揭示了其固有的脉动转矩对低速运动控制产生不利影响的动力学特征,并将它归结为两种结构不确定性,便于控制器的设计;其次,采取标准的自适应控制及其鲁棒化设计思想,借助于μ-修整策略来实现相应的控制律,确保脉动转矩的最大化补偿及伺服系统低速跟踪控制满足高性能的要求;最后对所建立的低速跟踪控制系统的性能进行了试验评估,并与作者前期的工作进行了比较,试验结果验证了其有效性与可行性.  相似文献   

甘蔗种质耐寒性试验研究     

马丽  范源洪  王丽萍  蔡青  夏红明 《亚热带农业研究》2003,10(2):6-10

11 3个甘蔗种质剥芽后浸泡于冷水中 2 4小时 ,并在 - 3℃低温下处理 1 2小时后定植于田间 ,根据低温处理后萌芽率的高低确定耐寒性强弱。结果表明 :1 1 3个材料中 ,耐寒性强的 2 8个 ,中等的 5 4个 ,弱的 31个  相似文献   

Isotopic composition of nitrogen: implications for the past history of mars' atmosphere     

McElroy MB  Yung YL  Nier AO 《Science (New York, N.Y.)》1976,194(4260):70-72

Models are presented for the past history of nitrogen on Mars based on Viking measurements showing that the atmosphere is enriched in (15)N. The enrichment is attributed to selective escape, with fast atoms formed in the exosphere by electron impact dissociation of N(2) and by dissociative recombination of N(2)(+). The initial partial pressure of N(2) should have been at least as large as several millibars and could have been as large as 30 millibars if surface processes were to represent an important sink for atmospheric HNO(2) and HNO(3).  相似文献   

Response: the loss of atmosphere from Mars     

Kass DM  Yung YL 《Science (New York, N.Y.)》1996,274(5294):1932b-1933b

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Developmentally regulated activation of a SINE B2 repeat as a domain boundary in organogenesis   总被引：1，自引：0，他引：1  

Lunyak VV  Prefontaine GG  Núñez E  Cramer T  Ju BG  Ohgi KA  Hutt K  Roy R  García-Díaz A  Zhu X  Yung Y  Montoliu L  Glass CK  Rosenfeld MG 《Science (New York, N.Y.)》2007,317(5835):248-251

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Greenhouse Effects due to Man-Mad Perturbations of Trace Gases     

Wang WC  Yung YL  Lacis AA  Mo T  Hansen JE 《Science (New York, N.Y.)》1976,194(4266):685-690

Nitrous oxide, methane, ammonia, and a number of other trace constituents in the earth's atmosphere have infrared absorption bands in the spectral region 7 to 14 microm and contribute to the atmospheric greenhouse effect. The concentrations of these trace gases may undergo substantial changes because of man's activities. Extensive use of chemical fertilizers and combustion of fossil fuels may perturb the nitrogen cycle, leading to increases in atmospheric N(2)O, and the same perturbing processes may increase the amounts of atmospheric CH(4) and NH(3). We use a one-dimensional radiative-convective model for the atmospheric thermal structure to compute the change in the surface temperature of the earth for large assumed increases in the trace gas concentrations; doubling the N(2)O, CH(4), and NH(3) concentrations is found to cause additive increases in the surface temperature of 0.7 degrees , 0.3 degrees , and 0.1 degrees K, respectively. These systematic effects on the earth's radiation budget would have substantial climatic significance. It is therefore important that the abundances of these trace gases be accurately monitored to determine the actual trends of their concentrations.  相似文献